Physical quantity detection circuit, physical quantity sensor, electronic instrument, vehicle, and method for diagnosing failure of physical quantity sensor

ABSTRACT

A physical quantity detection circuit including a differential amplification circuit that differentially amplifies a signal pair based on a first signal containing a first physical quantity component and a first vibration leakage component and a second signal containing a second physical quantity component having a phase opposite the phase of the first physical quantity component and a second vibration leakage component having the same phase as the phase of the first vibration leakage component, an adder circuit that adds the signal pair, a first synchronous wave-detection circuit that performs synchronous wave-detection on a signal based on an output signal from the differential amplification circuit, a second synchronous wave-detection circuit that performs synchronous wave-detection on a signal based on an output signal from the adder circuit, a physical quantity detection signal generation circuit that generates a physical quantity detection signal based on an output signal from the first synchronous wave-detection circuit, and a vibration leakage signal generation circuit that generates a vibration leakage signal based on an output signal from the second synchronous wave-detection circuit.

The present application is based on, and claims priority from JPApplication Serial Number 2019-081621, filed Apr. 23, 2019, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a physical quantity detection circuit,a physical quantity sensor, an electronic instrument, a vehicle, and amethod for diagnosing failure of the physical quantity sensor.

2. Related Art

At present, a physical quantity sensor capable of detecting a variety ofphysical quantities, such as a gyro sensor that detects angular velocityand an acceleration sensor that detects acceleration, are widely used ina variety of systems and electronic instruments. In recent years, toachieve high reliability in a system using a physical quantity sensor,an approach to diagnosis of whether or not the physical quantity sensorhas failed has been proposed.

For example, JP-A-2010-107416 describes a physical quantity detectionapparatus including a physical quantity detection circuit that detectsleakage vibration that occurs at two detection vibration arms of aphysical quantity detection device resulting from flexural vibration oftwo drive vibration arms and outputs signals according to the magnitudesof the leakage vibration in an abnormality diagnosis mode. Specifically,in the physical quantity detection circuit of the physical quantitydetection apparatus described in JP-A-2010-107416, in a physicalquantity detection mode, a differential amplification circuitdifferentially amplifies signals outputted from two detection electrodesof the physical quantity detection device, and a synchronouswave-detection circuit performs synchronous wave-detection on thedifferentially amplified signals, thereby the physical quantitydetection circuit generates signals according to physical quantitycomponents, whereas in an abnormality diagnosis mode, the differentialamplification circuit and the synchronous wave-detection circuit areused to change the phases of wave-detection signals inputted to thesynchronous wave-detection circuit, and signals according to vibrationleakage components are outputted. When the physical quantity detectiondevice breaks or otherwise fails, the magnitudes of the leakagevibration change, resulting in a change in the magnitude of the signaloutputted from the physical quantity detection circuit in theabnormality diagnosis mode, whereby failure of the physical quantitysensor can be diagnosed based on the signal outputted from the physicalquantity detection circuit.

In the physical quantity detection apparatus described inJP-A-2010-107416, however, the physical quantity detection device is sotuned that the vibration leakage components contained in the signalsoutputted from the two detection electrodes have opposite phases, andthe output signals from the differential amplification circuit eachcontain the physical quantity component and the vibration leakagecomponent that is relatively large. Therefore, in the physical quantitydetection mode, when the phase of the wave-detection signal deviatesfrom a design value due, for example, to manufacture variation, theoutput signal from the synchronous wave-detection circuit contains arelatively large vibration leakage component. Therefore, in the physicalquantity detection mode, a noise component contained in the signaloutputted from the physical quantity detection circuit increases, and azero point that is the magnitude of the physical quantity detectionsignal generated when no physical quantity acts could deviate from adesign value by an indefinite amount.

SUMMARY

An aspect of a physical quantity detection circuit according to thepresent disclosure is a physical quantity detection circuit thatgenerates a physical quantity detection signal according to a physicalquantity detected with a physical quantity detection device based on afirst signal and a second signal outputted from the physical quantitydetection device that detects the physical quantity, the first signalcontaining a first physical quantity component based on the physicalquantity detected with the physical quantity detection device and afirst vibration leakage component based on vibration of the physicalquantity detection device, the second signal containing a secondphysical quantity component based on the physical quantity detected withthe physical quantity detection device and a second vibration leakagecomponent based on the vibration of the physical quantity detectiondevice, the first and second physical quantity components havingopposite phases, and the first and second vibration leakage componentshaving the same phase, the physical quantity detection circuit includinga differential amplification circuit that differentially amplifies asignal pair based on the first and second signals, an adder circuit thatadds the signal pair, a first synchronous wave-detection circuit thatperforms synchronous wave-detection on a signal based on an outputsignal from the differential amplification circuit and outputs a signalaccording to a difference between the first physical quantity componentand the second physical quantity component, a second synchronouswave-detection circuit that performs synchronous wave-detection on asignal based on an output signal from the adder circuit and outputs asignal according to a sum of the first vibration leakage component andthe second vibration leakage component, a physical quantity detectionsignal generation circuit that generates the physical quantity detectionsignal based on an output signal from the first synchronouswave-detection circuit, and a vibration leakage signal generationcircuit that generates a vibration leakage signal based on an outputsignal from the second synchronous wave-detection circuit.

In the aspect of the physical quantity detection circuit, an amount ofdifference between the first vibration leakage component and the secondvibration leakage component may be substantially zero.

In the aspect of the physical quantity detection circuit, the physicalquantity detection circuit may further include a first chargeamplification circuit to which the first signal is inputted and a secondcharge amplification circuit to which the second signal is inputted, andthe signal pair may be formed of an output signal from the first chargeamplification circuit and an output signal from the second chargeamplification circuit.

In the aspect of the physical quantity detection circuit, the physicalquantity detection circuit may further include a failure diagnosiscircuit that performs failure diagnosis based on the vibration leakagesignal.

In the aspect of the physical quantity detection circuit, the failurediagnosis circuit may diagnose a state of the physical quantitydetection circuit as failure when a magnitude of the vibration leakagesignal does not fall within a first range.

In the aspect of the physical quantity detection circuit, the firstrange may be variable.

An aspect of a physical quantity sensor according to the presentdisclosure includes the physical quantity detection circuit according tothe aspect described above and the physical quantity detection device.

An aspect of an electronic instrument according to the presentdisclosure includes the physical quantity sensor according to the aspectdescribed above and a processing circuit that carries out a processbased on an output signal from the physical quantity sensor.

An aspect of a vehicle according to the present disclosure includes thephysical quantity sensor according to the aspect described above and aprocessing circuit that carries out a process based on an output signalfrom the physical quantity sensor.

An aspect of a method for diagnosing failure of a physical quantitysensor according to the present disclosure is a method for diagnosingfailure of a physical quantity sensor including a physical quantitydetection device that detects a physical quantity and outputs a firstsignal and a second signal and a physical quantity detection circuitthat generates a physical quantity detection signal according to thephysical quantity detected with the physical quantity detection devicebased on the first and second signals, the first signal containing afirst physical quantity component based on the physical quantitydetected with the physical quantity detection device and a firstvibration leakage component based on vibration of the physical quantitydetection device, the second signal containing a second physicalquantity component based on the physical quantity detected with thephysical quantity detection device and a second vibration leakagecomponent based on the vibration of the physical quantity detectiondevice, the first and second physical quantity components havingopposite phases, and the first and second vibration leakage componentshaving the same phase, the method including a differential amplificationstep of differentially amplifying a signal pair based on the first andsecond signals outputted from the physical quantity detection device, anadding step of adding the signal pair, a first synchronouswave-detection step of performing synchronous wave-detection on a signalbased on a signal obtained in the differential amplification step togenerate a signal according to a difference between the first physicalquantity component and the second physical quantity component, a secondsynchronous wave-detection step of performing synchronous wave-detectionon a signal based on a signal obtained in the adding step to generate asignal according to a sum of the first vibration leakage component andthe second vibration leakage component, a physical quantity detectionsignal generation step of generating the physical quantity detectionsignal based on a signal generated in the first synchronouswave-detection step, a vibration leakage signal generation step ofgenerating a vibration leakage signal based on a signal generated in thesecond synchronous wave-detection step, and a failure diagnosis step ofdiagnosing failure of the physical quantity sensor based on thevibration leakage signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a physical quantity sensoraccording to an embodiment of the present disclosure.

FIG. 2 is a plan view of a vibration element of a gyro sensor device.

FIG. 3 describes the action of the gyro sensor device.

FIG. 4 describes the action of the gyro sensor device.

FIG. 5 shows an example of the configuration of a drive circuit.

FIG. 6 shows an example of the configuration of a detection circuit.

FIG. 7 shows an example of the waveforms of a variety of signalscarrying physical quantity components contained in an output signal froma physical quantity detection device.

FIG. 8 shows an example of the waveforms of the variety of signalscarrying vibration leakage components contained in the output signalfrom the physical quantity detection device.

FIG. 9 is a flowchart showing an example of the procedure of a failurediagnosis method according to the present embodiment.

FIG. 10 is a functional block diagram showing an example of theconfiguration of an electronic instrument according to the presentembodiment.

FIG. 11 is a perspective view diagrammatically showing a digital camerathat is an example of the electronic instrument.

FIG. 12 shows an example of a vehicle according to the presentembodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A preferable embodiment of the present disclosure will be describedbelow in detail with reference to the drawings. It is not intended thatthe embodiment described below unduly limits the contents of the presentdisclosure set forth in the appended claims. Further, all configurationsdescribed below are not necessarily essential configuration requirementsof the present disclosure.

The following description will be made with reference to a physicalquantity sensor that detects angular velocity as a physical quantity,that is, an angular velocity sensor.

1. Physical Quantity Sensor 1-1. Configuration of Physical QuantitySensor

FIG. 1 is a functional block diagram of the physical quantity sensoraccording to the present embodiment. A physical quantity sensor 1according to the present embodiment includes a physical quantitydetection device 100, which detects a physical quantity, and a physicalquantity detection circuit 200.

The physical quantity detection device 100 includes a vibration elementon which drive electrodes and detection electrodes are disposed, and thevibration element is, in general, encapsulated in a package that ensureshermeticity thereof to increase the oscillation efficiency of thevibration element by minimizing the impedance thereof. In the presentembodiment, the physical quantity detection device 100 includes what iscalled a double-T-shaped vibration element having two T-shaped drivevibration arms.

FIG. 2 is a plan view of the vibration element of the physical quantitydetection device 100 in the present embodiment. The physical quantitydetection device 100 includes a double-T-shaped vibration elementformed, for example, of a Z-cut quartz crystal substrate. A vibrationelement made of quartz crystal advantageously allows an increase inangular velocity detection accuracy because the resonance frequencyvaries by only a very small amount versus a change in temperature. AxesX, Y, and Z in FIG. 2 represent quartz crystal axes.

The vibration element of the physical quantity detection device 100 hasdrive vibration arms 101 a and 101 b extending from two drive bases 104a and 104 b, respectively, in the +Y-axis and −Y-axis directions, asshown in FIG. 2. A drive electrode 112 and drive electrodes 113 areformed on the side surface and the upper surfaces of the drivevibrations arms 101 a, respectively, and a drive electrode 113 and driveelectrodes 112 are formed on the side surface and the upper surfaces ofthe drive vibrations arms 101 b, respectively. The drive electrodes 112and 113 are coupled to a drive circuit 20 via terminals DS and DG of thephysical quantity detection circuit 200 shown in FIG. 1.

The drive bases 104 a and 104 b are coupled to a rectangular detectionbase 107 via linkage arms 105 a and 105 b extending in the −X-axis and+X-axis directions, respectively.

Detection vibration arms 102 extend from the detection base 107 in the+Y-axis and −Y-axis directions. Detection electrodes 114 and 115 areformed on the upper surfaces of the detection vibration arms 102, andcommon electrodes 116 are formed on the side surfaces of the detectionvibration arms 102. The detection electrodes 114 and 115 are coupled toa detection circuit 30 via terminals S1 and S2 of the physical quantitydetection circuit 200 shown in FIG. 1, respectively. The commonelectrodes 116 are grounded.

When AC voltage is applied as a drive signal to the space between eachof the drive electrodes 112 and 113 of each of the drive vibration arms101 a and 101 b, the inverse piezoelectric effect causes the drivevibration arms 101 a and 101 b to undergo flexural vibration that causesthe tip ends of the two drive vibration arms 101 a and 101 b torepeatedly approach each other and separate from each other, asindicated by the arrows B shown in FIG. 3. The flexural vibration of thedrive vibration arms 101 a and 101 b is hereinafter also referred to as“excited vibration” in some cases.

In this state, when angular velocity around the axis Z acts on thevibration element of the physical quantity detection device 100, thedrive vibration arms 101 a and 101 b receive Coriolis force in thedirection perpendicular to both the flexural vibration directionindicated by the arrows B and the axis Z. As a result, the linkage arms105 a and 105 b vibrate as indicated by the arrows C, as shown in FIG.4. The detection vibration arms 102 then undergo flexural vibration asindicated by the arrows D together with the vibration of the linkagearms 105 a and 105 b. The flexural vibration of the detection vibrationarms 102 in association with the Coriolis force and the flexuralvibration of the drive vibration arms 101 a and 101 b are out of phaseby 90°.

When the two drive vibration arms 101 a and 101 b have the samemagnitude of vibration energy or the same magnitude of the amplitude ofthe vibration when the drive vibration arms 101 a and 101 b undergo theflexural vibration, the drive vibration arms 101 a and 101 b arebalanced with each other in terms of vibration energy thereof, so thatthe detection vibration arms 102 undergo no flexural vibration in astate in which no angular velocity acts on the physical quantitydetection device 100. When the balance of the vibration energy betweenthe two drive vibration arms 101 a and 10 ab deteriorates, however, thedetection vibration arms 102 undergo the flexural vibration even in thestate in which no angular velocity acts on the physical quantitydetection device 100. The flexural vibration in this state is calledleakage vibration and is flexural vibration indicated by the arrows Dsimilar to the vibration based on the Coriolis force but has a phaseshifted by 90° from the phase of the vibration based on the Coriolisforce.

The piezoelectric effect causes AC charge based on the flexuralvibration described above to be produced as the detection electrodes 114and 115 on the detection vibration arms 102. The AC charge producedbased on the Coriolis force changes in accordance with the magnitude ofthe Coriolis force, that is, the magnitude of the angular velocityacting on the physical quantity detection device 100. On the other hand,AC charge produced based on the leakage vibration is fixed irrespectiveof the magnitude of the angular velocity acting on the physical quantitydetection device 100.

Rectangular weight sections 103, which are wider than the drivevibration arms 101 a and 101 b, are formed at the tip ends of the drivevibration arms 101 a and 101 b. Forming the weight sections 103 at thetip ends of the drive vibration arms 101 a and 101 b allows an increasein the Coriolis force and relatively short vibration arms having adesired resonance frequency. Similarly, weight sections 106 wider thanthe detection vibration arms 102 are formed at the tip ends of thedetection vibration arms 102. Forming the weight sections 106 at the tipends of the detection vibration arms 102 allows an increase in the ACcharge produced at the detection electrodes 114 and 115.

As described above, the physical quantity detection device 100 outputsthe AC charge based on the detected physical quantity and the AC chargebased on the leakage vibration out of the excited vibration via thedetection electrodes 114 and 115. The AC charge based on a physicalquantity is hereinafter referred to as a “physical quantity component,”and the AC charge based on the leakage vibration is hereinafter referredto as a “vibration leakage component” in some cases. In the presentembodiment, the physical quantity detected by the physical quantitydetection device 100 is angular velocity according to the Coriolisforce.

Referring back to the description with reference to FIG. 1, the physicalquantity detection circuit 200 includes a reference voltage circuit 10,the drive circuit 20, the detection circuit 30, an analog/digitalconversion circuit 41, an analog/digital conversion circuit 42, adigital signal processing circuit 51, a digital signal processingcircuit 52, a failure diagnosis circuit 60, an interface circuit 70, astorage 80, and an oscillation circuit 90. The physical quantitydetection circuit 200 may be achieved, for example, by a one-chipintegrated circuit (IC). The physical quantity detection circuit 200 mayinstead be so configured that part of the elements described above isomitted or changed or another element is added to the elements describedabove.

The reference voltage circuit 10 produces fixed voltage or fixedcurrent, such as reference voltage that is analog ground voltage, basedon power supply voltage and ground voltage supplied via terminals VDDand VSS of the physical quantity detection circuit 200 and supplies thedrive circuit 20 and the detection circuit 30 with the fixed voltage orcurrent.

The drive circuit 20 generates the drive signal for causing the physicalquantity detection device 100 to undergo the excited vibration andsupplies the drive electrodes 112 on the physical quantity detectiondevice 100 via the terminal DS. The drive circuit 20 receivesoscillation current produced at the drive electrodes 113 by the excitedvibration of the physical quantity detection device 100 via the terminalDG and performs feedback control on the amplitude level of the drivesignal in such a way that the amplitude of the oscillation current isheld at a fixed value. Further, the drive circuit 20 generates awave-detection signal SDET having the same phase as that of the drivesignal and a wave-detection signal QDET having a phase different by 90°from that of the drive signal and outputs the wave-detection signalsSDET and QDET to the detection circuit 30.

The detection circuit 30 receives the AC charges produced at the twodetection electrodes 114 and 115 on the physical quantity detectiondevice 100 via the terminals S1 and S2 of the physical quantitydetection circuit 200, respectively, uses the wave-detection signal SDETto detect the physical quantity components contained in the AC charges,and generates and outputs a physical quantity detection signal SAO,which is an analog signal having a voltage level according to themagnitudes of the physical quantity components. Further, the detectioncircuit 30 detects the vibration leakage components contained in the ACcharges inputted via the terminals S1 and S2 and generates and outputs avibration leakage signal QAO, which is an analog signal having a voltagelevel according to the magnitudes of the vibration leakage components.

The storage 80 includes a nonvolatile memory that is not shown, and thenonvolatile memory stores a variety of trimming data for the drivecircuit 20 and the detection circuit 30, for example, adjustment dataand correction data. The nonvolatile memory may be formed, for example,of a MONOS (metal oxide nitride oxide silicon) memory or an EEPROM(electrically erasable programmable read-only memory). Further, thestorage 80 may include a register that is not shown, and when thephysical quantity detection circuit 200 is powered on, that is, when thevoltage at the terminal VDD rises from 0 V to desired voltage, thevariety of trimming data stored in the nonvolatile memory may betransferred and held in the register, and the variety of trimming dataheld in the register may be supplied to the drive circuit 20 and thedetection circuit 30.

The analog/digital conversion circuit 41 operates based on a clocksignal ADCLK, converts the physical quantity detection signal SAO, whichis an analog signal, into a physical quantity detection signal SDO,which is a digital signal, and outputs the physical quantity detectionsignal SDO.

The analog/digital conversion circuit 42 operates based on the clocksignal ADCLK, converts the vibration leakage signal QAO, which is ananalog signal, into a vibration leakage signal QDO, which is a digitalsignal, and outputs the vibration leakage signal QDO.

The digital signal processing circuit 51 operates based on a masterclock signal MCLK, performs predetermined computation on the physicalquantity detection signal SDO outputted from the analog/digitalconversion circuit 41, and outputs a physical quantity detection signalSDOX provided by the computation.

The digital signal processing circuit 52 operates based on the masterclock signal MCLK, performs predetermined computation on the vibrationleakage signal QDO outputted from the analog/digital conversion circuit42, and outputs a vibration leakage signal QDOX provided by thecomputation.

The failure diagnosis circuit 60 operates based on the master clocksignal MCLK and diagnoses failure of the physical quantity sensor 1based on the vibration leakage signal QDOX. The failure diagnosiscircuit 60 then outputs a failure diagnosis result signal QFrepresenting whether or not the physical quantity sensor 1 has failed.When the physical quantity sensor 1 operates normally, the magnitude ofthe vibration leakage signal QDOX falls within a predetermined range. Incontrast, for example, when part of the physical quantity detectiondevice 100 breaks, when part of a wiring line electrically coupled tothe detection electrode 114 on the physical quantity detection device100 is cut and decoupled or short-circuited, or when part of a wiringline electrically coupled to the detection electrode 115 on the physicalquantity detection device 100 is cut and decoupled or short-circuited,the magnitude of the vibration leakage signal QDOX does not falls withinthe predetermined range. The failure diagnosis circuit 60 may thereforediagnose the state of the physical quantity sensor 1 as failure when themagnitude of the vibration leakage signal QDOX does not fall within afirst range. For example, the first range may be so set as to contain adesign value of the vibration leakage signal QDOX and further contain arange over which the vibration leakage signal QDOX deviates from thedesign value over time. The first range may be fixed or may vary. Forexample, the first range may be so set as to vary in accordance with avalue stored in the register, which is provided in the storage 80 and isrewritable by a component external to the physical quantity detectioncircuit 200.

The interface circuit 70 outputs the physical quantity detection signalSDOX outputted from the digital signal processing circuit 51 and thefailure diagnosis result signal QF to a micro control unit (MCU) 5,which is an apparatus external to the physical quantity detectioncircuit 200, in accordance with a request from the MCU 5. The interfacecircuit 70 may further output the vibration leakage signal QDOXoutputted from the digital signal processing circuit 52 to the MCU 5 inaccordance with a request from the MCU 5. The interface circuit 70 readsand outputs the data stored in the nonvolatile memory or the register ofthe storage 80 to the MCU 5 and writes data inputted from the MCU 5 ontothe nonvolatile memory or the register of the storage 80. For example,the MCU 50 may write the value for setting the first range describedabove onto a predetermined register.

The interface circuit 70 is, for example, an SPI-(serial peripheralinterface)-bus-based interface circuit, receives a selection signal, aclock signal, and a data signal transmitted from the MCU 5 via terminalsSS, SCLK, and SI of the physical quantity detection circuit 200, andoutputs a data signal to the MCU 5 via a terminal SO of the physicalquantity detection circuit 200. The interface circuit 70 may instead bean interface circuit that handles a variety of buses excluding an SPIbus, for example, an I²C (inter-integrated circuit) bus.

The oscillation circuit 90 produces the master clock signal MCLK andsupplies the digital signal processing circuits 51 and 52 and thefailure diagnosis circuit 60 with the master clock signal MCLK. Theoscillation circuit 90 further divides the master clock signal MCLK byan integer to generate the clock signal ADCLK and supplies theanalog/digital conversion circuits 41 and 42 with the clock signalADCLK. The oscillation circuit 90 may generate the master clock signalMCLK, for example, by using a ring oscillator or a CR oscillationcircuit.

In the thus configured physical quantity sensor 1, the physical quantitydetection device 100 outputs a first signal carrying the AC chargeproduced at the detection electrode 114 and a second signal carrying theAC charge produced at the detection electrode 115, and the physicalquantity detection circuit 200 generates the physical quantity detectionsignal SDOX according to the physical quantity detected with thephysical quantity detection device 100 based on the first and secondsignals outputted from the physical quantity detection device 100.

1-2. Configuration of Drive Circuit

FIG. 5 shows an example of the configuration of the drive circuit 20.The drive circuit 20 includes a current-voltage conversion circuit 21,an AC amplification circuit 22, an amplitude adjustment circuit 23, anda phase shift circuit 24, as shown in FIG. 5.

The oscillation current produced at the drive electrodes 113 by theexcited vibration of the physical quantity detection device 100 isinputted to the current-voltage conversion circuit 21 via the terminalDG and converted by the current-voltage conversion circuit 21 into an ACvoltage signal. The AC voltage signal outputted from the current-voltageconversion circuit 21 is inputted to the AC amplification circuit 22 andthe amplitude adjustment circuit 23.

The AC amplification circuit 22 amplifies the inputted AC voltagesignal, clips the amplified AC voltage signal at a predetermined voltagevalue, and outputs the resultant square-wave drive signal. The amplitudeadjustment circuit 23 changes the amplitude of the drive signal inaccordance with the level of the AC voltage signal outputted by thecurrent-voltage conversion circuit 21 to control the AC amplificationcircuit 22 in such a way that the amplitude of the oscillation currentis held at a fixed value.

The drive signal outputted from the AC amplification circuit 22 issupplied to the drive electrodes 112 on the physical quantity detectiondevice 100 via the terminal DS. The physical quantity detection device100 to which the drive signal is supplied can continue the excitedvibration. Further, keeping the oscillation current fixed allows thedrive vibration arms 101 a and 101 b of the physical quantity detectiondevice 100 to vibrate at a fixed vibration speed. The vibration speedbased on which the Coriolis force is produced is therefore fixed,whereby the sensitivity of the physical quantity sensor 1 can be morestabilized.

The AC amplification circuit 22 outputs the wave-detection signal SDET,which is a square wave and has the same phase as that of the drivesignal, and the phase shift circuit 24 outputs the wave-detection signalQDET, the phase of which advances by 90° with respect to the phase ofthe wave-detection signal SDET. The wave-detection signals SDET and QDETare supplied to the detection circuit 30.

1-3. Configuration of Detection Circuit

FIG. 6 shows an example of the configuration of the detection circuit30. The detection circuit 30 includes charge amplification circuits 31Aand 31B, a differential amplification circuit 32, an adder circuit 33,AC amplification circuits 34A and 34B, synchronous wave-detectioncircuits 35A and 35B, smoothening circuits 36A and 36B, variableamplification circuits 37A and 37B, and filter circuits 38A and 38B, asshown in FIG. 6.

The first signal is inputted to the charge amplification circuit 31A viathe terminal S1. The first signal carries the AC charge produced at thedetection electrode 114 on the physical quantity detection device 100and contains a first physical quantity component based on the physicalquantity detected by the physical quantity detection device 100 and afirst vibration leakage component based on the vibration of the physicalquantity detection device 100.

The second signal is inputted to the charge amplification circuit 31Bvia the terminal S2. The second signal carries the AC charge produced atthe detection electrode 115 on the physical quantity detection device100 and contains a second physical quantity component based on thephysical quantity detected by the physical quantity detection device 100and a second vibration leakage component based on the vibration of thephysical quantity detection device 100.

In the present embodiment, when angular velocity acts on the physicalquantity detection device 100, the detection vibration arm 102 on whichthe detection electrode 114 is formed and the detection vibration arm102 on which the detection electrode 115 is formed undergo flexuralvibration in opposite directions in a balanced manner. The first andsecond physical quantity components therefore have opposite phases. Thecase where the first and second physical quantity components haveopposite phases is not limited to the case where the difference in phasebetween the first and second physical quantity components is exactly180° and also includes a case where the difference in phase between thefirst and second physical quantity components deviates from 180° by avery small amount due, for example, to errors in the manufacture of thephysical quantity detection device 100 and errors in delay time thatoccurs along the signal propagation path.

In the present embodiment, the first and second vibration leakagecomponents have the same phase. The case where the first and secondvibration leakage components have the same phase is not limited to thecase where the difference in phase between the first and secondvibration leakage components is exactly 0° and also includes a casewhere the difference in phase between the first and second vibrationleakage components deviates from 0° by a very small amount due, forexample, to errors in the manufacture of the physical quantity detectiondevice 100 and errors in delay time that occurs along the signalpropagation path.

For example, tuning the weights of the four weight sections 103 in sucha way that the two drive vibration arms 101 a have the same vibrationenergy, that the two drive vibration arms 101 b have the same vibrationenergy, and that the total vibration energy of the two drive vibrationarms 101 a differs from the total vibration energy of the two drivevibration arms 101 b allows the first and second vibration leakagecomponents to have the same phase. The greater the difference betweenthe total vibration energy of the two drive vibration arms 101 a and thetotal vibration energy of the two drive vibration arms 101 b, thegreater the first and second vibration leakage components. The weightsof the weight sections 103 can be tuned, for example, by irradiatingeach of the weight sections 103 with a laser beam to cut part of theweight section 103.

The charge amplification circuit 31A converts the first signal into anAC voltage signal defined with respect to reference voltage V_(ref)produced by the reference voltage circuit 10 and outputs the AC voltagesignal, and the charge amplification circuit 31B converts the secondsignal into an AC voltage signal defined with respect to the referencevoltage V_(ref) and outputs the AC voltage signal. The chargeamplification circuit 31A is an example of a “first charge amplificationcircuit,” and the charge amplification circuit 31B is an example of a“second charge amplification circuit.”

The differential amplification circuit 32 differentially amplifies thesignal pair formed of the output signals from the charge amplificationcircuits 31A and 31B. The signal pair is a signal pair based on thefirst and second signals. Since the first and second physical quantitycomponents have opposite phases, as described above, the differentialamplification circuit 32 amplifies the physical quantity components. Onthe other hand, since the first and second vibration leakage componentshave the same phase, the differential amplification circuit 32attenuates the vibration leakage components. Therefore, in the outputsignal from the differential amplification circuit 32, the influence ofthe vibration leakage components on the physical quantity componentsdecreases. To substantially eliminate the influence of the vibrationleakage components on the physical quantity components in the outputsignal from the differential amplification circuit 32, the amount ofdifference between the first and second vibration leakage components isdesirably substantially zero. The case where the amount of differencebetween the first and second vibration leakage components issubstantially zero is not limited to a case where the amount ofdifference is exactly zero and includes a case where the amount ofdifference deviates from zero by a very small amount due, for example,to the minimum adjustment resolution of the first and second vibrationleakage components and a case where a measured value of the amount ofdifference between the first and second vibration leakage componentsdeviates from zero by a very small amount due to an error in measurementof the amount of the difference.

The AC amplification circuit 34A amplifies the output signal from thedifferential amplification circuit 32. The output signal from the ACamplification circuit 34A is inputted to the synchronous wave-detectioncircuit 35A.

The synchronous wave-detection circuit 35A performs synchronous wavedetection on the output signal from the AC amplification circuit 34A asa wave detection target signal by using the wave-detection signal SDET.The synchronous wave-detection circuit 35A extracts the physicalquantity component contained in the output signal from the ACamplification circuit 34A. That is, the synchronous wave-detectioncircuit 35A performs synchronous wave detection on the output signalfrom the AC amplification circuit 34A, which is a signal based on theoutput signal from the differential amplification circuit 32, andoutputs a signal according to the difference between the first physicalquantity component contained in the first signal and the second physicalquantity component contained in the second signal. The synchronouswave-detection circuit 35A may, for example, be a switch circuit thatselects the output signal from the AC amplification circuit 34A when thevoltage level of the wave-detection signal SDET is higher than thereference voltage V_(ref) and selects the output signal outputted fromthe AC amplification circuit 34A but reversed with respect to thereference voltage V_(ref) when the voltage level of the wave-detectionsignal SDET is lower than the reference voltage V_(ref). The synchronouswave-detection circuit 35A is an example of a “first synchronouswave-detection circuit.”

The output signal from the synchronous wave-detection circuit 35A issmoothened by the smoothening circuit 36A into a DC voltage signal,which is then inputted to the variable amplification circuit 37A.

The variable amplification circuit 37A amplifies or attenuates theoutput signal from the smoothening circuit 36A by using a set gain toadjust the detection sensitivity of the physical quantity sensor 1. Thesignal amplified or attenuated by the variable amplification circuit 37Ais inputted to the filter circuit 38A.

The filter circuit 38A is a circuit that limits the frequency of theoutput signal from the variable amplification circuit 37A to a frequencythat belongs to a desired frequency band. The output signal from thefilter circuit 38A is outputted as the physical quantity detectionsignal SAO from the detection circuit 30.

The smoothening circuit 36A, the variable amplification circuit 37A, thefilter circuit 38A, the analog/digital conversion circuit 41, and thedigital signal processing circuit 51 are circuits that generate thephysical quantity detection signal SDOX based on the output signal fromthe synchronous wave-detection circuit 35A and are an example of a“physical quantity detection signal generation circuit.”

The adder circuit 33 adds the signal pair formed of the output signalfrom the charge amplification circuit 31A to the output signal from thecharge amplification circuit 31B. Since the first and second physicalquantity components have opposite phases, as described above, the addercircuit 33 attenuates the physical quantity components. On the otherhand, since the first and second vibration leakage components have thesame phase, the adder circuit 33 amplifies the vibration leakagecomponents.

The AC amplification circuit 34B amplifies the output signal from theadder circuit 33. The output signal from the AC amplification circuit34B is inputted to the synchronous wave-detection circuit 35B.

The synchronous wave-detection circuit 35B performs synchronous wavedetection on the output signal from the AC amplification circuit 34B asa wave detection target signal by using the wave-detection signal QDET.The synchronous wave-detection circuit 35B extracts the physicalquantity component contained in the output signal from the ACamplification circuit 34B. That is, the synchronous wave-detectioncircuit 35B performs synchronous wave detection on the output signalfrom the AC amplification circuit 34B, which is a signal based on theoutput signal from the adder circuit 33, and outputs a signal accordingto the sum of the first vibration leakage component contained in thefirst signal and the second vibration leakage component contained in thesecond signal. The synchronous wave-detection circuit 35B may, forexample, be a switch circuit that selects the output signal from the ACamplification circuit 34B when the voltage level of the wave-detectionsignal QDET is higher than the reference voltage V_(ref) and selects theoutput signal outputted from the AC amplification circuit 34B butreversed with respect to the reference voltage V_(ref) when the voltagelevel of the wave-detection signal QDET is lower than the referencevoltage V_(ref). The synchronous wave-detection circuit 35B is anexample of a “second synchronous wave-detection circuit.”

The output signal from the synchronous wave-detection circuit 35B issmoothened by the smoothening circuit 36B into a DC voltage signal,which is then inputted to the variable amplification circuit 37B.

The variable amplification circuit 37B amplifies or attenuates theoutput signal from the smoothening circuit 36B by using a set gain. Thesignal amplified or attenuated by the variable amplification circuit 37Bis inputted to the filter circuit 38B.

The filter circuit 38B is a circuit that limits the frequency of theoutput signal from the variable amplification circuit 37B to a frequencythat belongs to a desired frequency band. The output signal from thefilter circuit 38B is outputted as the vibration leakage signal QAO fromthe detection circuit 30.

The smoothening circuit 36B, the variable amplification circuit 37B, thefilter circuit 38B, the analog/digital conversion circuit 42, and thedigital signal processing circuit 52 are circuits that generate thevibration leakage signal QDOX based on the output signal from thesynchronous wave-detection circuit 35B and are an example of a“vibration leakage signal generation circuit.”

1-4. Example of Signal Waveforms

FIG. 7 shows an example of the waveforms of a variety of signalscarrying the physical quantity components contained in the AC chargesoutputted from the physical quantity detection device 100. FIG. 7 showsthe waveforms of the signals between the points A and C shown in FIG. 5and the waveforms of the signals between the points D and K shown inFIG. 6. The waveforms of the signals are drawn with the horizontal axisrepresenting the time and the vertical axis representing the voltage.FIG. 7 shows a case where fixed angular velocity acts on the physicalquantity detection device 100.

The signal at the point A is the output signal from the current-voltageconversion circuit 21 and is a fixed-frequency signal that changes withrespect to the reference voltage V_(ref) to values on opposite sidesthereof.

The signal at the point B is the output signal from the AC amplificationcircuit 22, that is, the wave-detection signal SDET, and is asquare-wave voltage signal having the same phase as that of the signalat the point A and having an amplitude of a fixed value V_(c).

The signal at the point C is the output signal from the phase shiftcircuit 24, that is, the wave-detection signal QDET, and is asquare-wave voltage signal having a phase that advances by 90° withrespect to the phase of the signal at the point B and having anamplitude of the fixed value V_(c).

The signal at the point D is a fixed-frequency signal that carries thefirst physical quantity component contained in the output signal fromthe charge amplifier circuit 31A, has the same phase as that of thesignal at the point A, and changes with respect to the reference voltageV_(ref) to values on opposite sides thereof.

The signal at the point E is a fixed-frequency signal that carries thesecond physical quantity component contained in the output signal fromthe charge amplifier circuit 31B, has a phase different from that of thesignal at the point A by 180°, and changes with respect to the referencevoltage V_(ref) to values on opposite sides thereof. The first physicalquantity component contained in the signal at the point D and the secondphysical quantity component contained in the signal at the point E haveopposite phases but substantially the same amplitude.

The signal at the point F is a fixed-frequency signal that carries thephysical quantity component contained in the output signal from the ACamplification circuit 34A, that is, the first physical quantitycomponent contained in the signal at the point D and the second physicalquantity component contained in the signal at the point R that aredifferentially amplified, has the same phase as that of the signal atthe point A, and changes with respect to the reference voltage V_(ref)to values on opposite sides thereof.

The signal at the point G is a signal that carries the physical quantitycomponent contained in the output signal from the synchronouswave-detection circuit 35A, that is, the physical quantity componentcontained in the signal at the point F but caused to undergo full-waverectification by using the signal at the point B with respect to thereference voltage V_(ref).

The signal at the point H is a signal that carries the physical quantitycomponent contained in the output signal from the filter circuit 38A andhas a voltage value V₁ according to the physical quantity detected bythe physical quantity detection device 100.

The signal at the point I is a signal that carries the physical quantitycomponent contained in the output signal from the AC amplificationcircuit 34B, that is, the first physical quantity component contained inthe signal at the point D and the second physical quantity componentcontained in the signal at the point E that are so summed up andamplified as to be substantially removed and has a voltage value equalto the reference voltage V_(ref).

The signal at the point J is a signal that carries the physical quantitycomponent contained in the output signal from the synchronouswave-detection circuit 35B, that is, the physical quantity componentcontained in the signal at the point I but caused to undergo full-waverectification by using the signal at the point C with respect to thereference voltage V_(ref) and has a voltage value equal to the referencevoltage V_(ref).

The signal at the point K is a signal that carries the physical quantitycomponent contained in the output signal from the filter circuit 38B andhas a voltage value equal to the reference voltage V_(ref).

FIG. 8 shows an example of the waveforms of the variety of signalscarrying the vibration leakage components contained in the AC chargesoutputted from the physical quantity detection device 100. FIG. 8 showsthe waveforms of the signals between the points A and C shown in FIG. 5and the waveforms of the signals between the points D and K shown inFIG. 6. The waveforms of the signals are drawn with the horizontal axisrepresenting the time and the vertical axis representing the voltage.

In FIG. 8, the signals at the points A, B, and C are the same as thosein FIG. 7.

The signal at the point D is a fixed-frequency signal that carries thefirst vibration leakage component contained in the output signal fromthe charge amplifier circuit 31A, has a phase that advances by 90° withrespect to the phase of the signal at the point A, and changes withrespect to the reference voltage V_(ref) to values on opposite sidesthereof.

The signal at the point E is a fixed-frequency signal that carries thesecond vibration leakage component contained in the output signal fromthe charge amplifier circuit 31B, has a phase that advances by 90° withrespect to the phase of the signal at the point A, and changes withrespect to the reference voltage V_(ref) to values on opposite sidesthereof. The first vibration leakage component contained in the signalat the point D and the second vibration leakage component contained inthe signal at the point E have the same phase and substantially the sameamplitude.

The signal at the point F is a signal that carries the vibration leakagecomponent contained in the output signal from the AC amplificationcircuit 34A, that is, the first vibration leakage component contained inthe signal at the point D and the second vibration leakage componentcontained in the signal at the point E that are differentially amplifiedas to be substantially removed and has a voltage value equal to thereference voltage V_(ref).

The signal at the point G is a signal that carries the vibration leakagecomponent contained in the output signal from the synchronouswave-detection circuit 35A, that is, the vibration leakage componentcontained in the signal at the point F but caused to undergo full-waverectification by using the signal at the point B with respect to thereference voltage V_(ref) and has a voltage value equal to the referencevoltage V_(ref).

The signal at the point H is a signal that carries the vibration leakagecomponent contained in the output signal from the filter circuit 38A andhas a voltage value equal to the reference voltage V_(ref).

The signal at the point I is a signal that carries the vibration leakagecomponent contained in the output signal from the AC amplificationcircuit 34B, that is, the first vibration leakage component contained inthe signal at the point D and the second vibration leakage componentcontained in the signal at the point E that are summed up and amplified,has a phase that advances by 90° with respect to the phase of the signalat the point A, and changes with respect to the reference voltageV_(ref) to values on opposite sides thereof.

The signal at the point J is a signal that carries the vibration leakagecomponent contained in the output signal from the synchronouswave-detection circuit 35B, that is, the vibration leakage componentcontained in the signal at the point I but caused to undergo full-waverectification by using the signal at the point C with respect to thereference voltage V_(ref).

The signal at the point K is a signal that carries the vibration leakagecomponent contained in the output signal from the filter circuit 38B andhas a voltage value V2 according to the vibration leakage that occurs atthe physical quantity detection device 100.

In practice, the signals at the points D to K each have the waveforms inFIG. 7 added to the waveforms in FIG. 8. Since the signal at the point Hin FIG. 8 is a signal having a voltage value equal to the referencevoltage V_(ref), the output signal from the filter circuit 38A, that is,the physical quantity detection signal SAO hardly contains a vibrationleakage component, substantially coincides with the signal at the pointH in FIG. 7, and is a signal having the voltage level according to thephysical quantity components. Therefore, the MCU 5 can measure thephysical quantity having acted on the physical quantity sensor 1 byreading the physical quantity detection signal SDOX generated based onthe physical quantity detection signal SAO.

Since the signal at the point K in FIG. 7 is a signal having a voltagevalue equal to the reference voltage V_(ref), the output signal from thefilter circuit 38B, that is, the vibration leakage signal QAO hardlycontains a physical quantity component, substantially coincides with thesignal at the point K in FIG. 8, and is a signal having the voltagelevel according to the vibration leakage components. When the physicalquantity sensor 1 operates normally, the vibration leakage signal QAOhas a substantially fixed voltage level. The failure diagnosis circuit60 can therefore diagnose the state of the physical quantity sensor 1 asfailure when the magnitude of the vibration leakage signal QDOXgenerated based on the vibration leakage signal QAO does not fall withinthe first range.

1-5. Procedure of Failure Diagnosis Method

FIG. 9 is a flowchart showing an example of the procedure of a methodfor diagnosing failure of the physical quantity sensor 1 according tothe present embodiment. In the flowchart shown in FIG. 9, the processesin the steps may be swapped as appropriate.

In the method for diagnosing failure of the physical quantity sensor 1according to the present embodiment, the charge amplifier circuits 31Aand 31B of the physical quantity detection circuit 200 first generate asignal pair based on the first and second signals outputted from thephysical quantity detection device 100 (step S1), as shown in FIG. 9.The first signal is a signal containing the first physical quantitycomponent based on a physical quantity detected with the physicalquantity detection device 100 and the first vibration leakage componentbased on the vibration of the physical quantity detection device 100,and the first signal is inputted to the charge amplifier circuit 31A viathe terminal S1. The second signal is a signal containing the secondphysical quantity component based on the physical quantity detected withthe physical quantity detection device 100 and the second vibrationleakage component based on the vibration of the physical quantitydetection device 100, and the second signal is inputted to the chargeamplifier circuit 31B via the terminal S2. The first and second physicalquantity components have opposite phases, as the signals at the points Dand E in FIG. 7. The first and second vibration leakage components havethe same phase, as the signals at the points D and E in FIG. 8.

The differential amplification circuit 32 of the physical quantitydetection circuit 200 then differentially amplifies the signal pairproduced in step S1 based on the first and second signals (step S2).

The synchronous wave-detection circuit 35A of the physical quantitydetection circuit 200 then performs synchronous wave-detection on asignal based on the signal generated in step S2 to generate a signalaccording to the difference between the first and second physicalquantity components (step S3).

The physical quantity detection signal generation circuit of thephysical quantity detection circuit 200 then generates the physicalquantity detection signal SDOX based on the signal generated in step S3(step S4). The physical quantity detection signal generation circuit isa circuit formed of the smoothening circuit 36A, the variableamplification circuit 37A, the filter circuit 38A, the analog/digitalconversion circuit 41, and the digital signal processing circuit 51.

The physical quantity detection circuit 200 carries out the processes insteps S5, S6, S7, and S8 concurrently with the processes in steps S2,S3, and S4.

Specifically, the adder circuit 33 of the physical quantity detectioncircuit 200 first adds the signal pair generated in step S1 based on thefirst and second signals (step S5).

The synchronous wave-detection circuit 35B of the physical quantitydetection circuit 200 then performs synchronous wave-detection on asignal based on the signal generated in step S5 to generate a signalaccording to the sum of the first and second vibration leakagecomponents (step S6).

The vibration leakage signal generation circuit of the physical quantitydetection circuit 200 then generates the vibration leakage signal QDOXbased on the signal generated in step S6 (step S7). The vibrationleakage signal generation circuit is a circuit formed of the smootheningcircuit 36B, the variable amplification circuit 37B, the filter circuit38B, the analog/digital conversion circuit 42, and the digital signalprocessing circuit 52.

The failure diagnosis circuit 60 of the physical quantity detectioncircuit 200 diagnoses failure of the physical quantity sensor 1 based onthe vibration leakage signal QDOX generated in step S7 (step S8).

The physical quantity detection circuit 200 then repeatedly carries outthe processes in steps S1 to S8.

Step S2 in FIG. 9 is an example of a “differential amplification step.”Step S3 in FIG. 9 is an example of a “first synchronous wave-detectionstep.” Step S4 in FIG. 9 is an example of a “physical quantity detectionsignal generation step.” Step S5 in FIG. 9 is an example of a “addingstep.” Step S6 in FIG. 9 is an example of a “second synchronouswave-detection step.” Step S7 in FIG. 9 is an example of a “vibrationleakage signal generation step.” Step S8 in FIG. 9 is an example of a“failure diagnosis step.”

1-6. Operational Effects

In the physical quantity sensor 1 according to the present embodiment,the physical quantity detection device 100 outputs the first signalcontaining the first physical quantity component based on a detectedphysical quantity and the first vibration leakage component based on thevibration of the physical quantity detection device 100 and the secondsignal containing the second physical quantity component based on thedetected physical quantity and the second vibration leakage componentbased on the vibration of the physical quantity detection device 100.The physical quantity detection circuit 200 includes the adder circuit33, which adds the signal pair based on the first and second signalsoutputted from the physical quantity detection device 100, thesynchronous wave-detection circuit 35B, which performs synchronouswave-detection on a signal based on the output signal from the addercircuit 33 and outputs a signal according to the sum of the first andsecond vibration leakage components, and the vibration leakage signalgeneration circuit that generates the vibration leakage signal QDOXbased on the output signal from the synchronous wave-detection circuit35B. Since the first and second vibration leakage components have thesame phase, the adder circuit 33 amplifies the vibration leakagecomponents. Further, for example, when part of the physical quantitydetection device 100 breaks or when part of a wiring line electricallycoupled to the physical quantity detection device 100 is cut anddecoupled or short-circuited, the magnitude of the first or secondvibration leakage component changes, and the magnitude of the vibrationleakage signal QDOX changes accordingly. The physical quantity sensor 1,the physical quantity detection circuit 200, or the method fordiagnosing failure of the physical quantity sensor 1 can thereforegenerate the vibration leakage signal QDOX usable for the failurediagnosis based on the leakage vibration that occurs at the physicalquantity detection device 100.

In the physical quantity sensor 1 according to the present embodiment,the physical quantity detection circuit 200 includes the differentialamplification circuit 32, which differentially amplifies the signal pairbased on the first and second signals outputted from the physicalquantity detection device 100, the synchronous wave-detection circuit35A, which performs synchronous wave-detection on a signal based on theoutput signal from the differential amplification circuit 32 and outputsa signal according to the difference between the first and secondphysical quantity components, and the physical quantity detection signalgeneration circuit that generates the physical quantity detection signalSDOX based on the output signal from the synchronous wave-detectioncircuit 35A. Since the first physical quantity component contained inthe first signal and the second physical quantity component contained inthe second signal have opposite phases, the differential amplificationcircuit 32 amplifies the physical quantity components. Further, sincethe magnitudes of the first and second physical quantity componentschange in accordance with the magnitude of the physical quantitydetected with the physical quantity detection device 100, the magnitudeof the physical quantity detection signal SDOX changes. The physicalquantity sensor 1, the physical quantity detection circuit 200, or themethod for diagnosing failure of the physical quantity sensor 1 cantherefore generate the physical quantity detection signal SDOX accordingto the physical quantity detected with the physical quantity detectiondevice 100.

In the physical quantity sensor 1 according to the present embodiment,since the first vibration leakage component contained in the firstsignal and the second vibration leakage component contained in thesecond signal have the same phase, the differential amplificationcircuit 32 attenuates the vibration leakage components. Therefore, evenwhen the phase of the wave-detection signal SDET inputted to thesynchronous wave-detection circuit 35A deviates from a design value due,for example, to manufacture variation, the vibration leakage componentcontained in the output signal from the synchronous wave-detectioncircuit 35A decreases, whereby a concern of an increase in the noisecomponent contained in the physical quantity detection signal SDOX and aconcern of deviation of the zero point from a design value by anindefinite amount are suppressed. The physical quantity sensor 1, thephysical quantity detection circuit 200, or the method for diagnosingfailure of the physical quantity sensor 1 can therefore lower theinfluence of the leakage vibration on the physical quantity detectionsignal SDOX. In particular, when the physical quantity detection device100 is so tuned that the amount of difference between the first andsecond vibration leakage components is substantially zero, the vibrationleakage component contained in the output signal from the differentialamplification circuit 32 is substantially zero. Therefore, even when thephase of the wave-detection signal SDET deviates from a design value,the output signal from the synchronous wave-detection circuit 35A hardlycontains a vibration leakage component, so that there is hardly aninfluence of the leakage vibration on the physical quantity detectionsignal SDOX.

In the physical quantity sensor 1 according to the present embodiment,since the first physical quantity component contained in the firstsignal and the second physical quantity component contained in thesecond signal have opposite phases, the adder circuit 33 attenuates thephysical quantity components. Therefore, even when the phase of thewave-detection signal QDET inputted to the synchronous wave-detectioncircuit 35B deviates from a design value due, for example, tomanufacture variation, the physical quantity component contained in theoutput signal from the synchronous wave-detection circuit 35B decreases,whereby a concern of an increase in the noise component contained in thevibration leakage signal QDOX is suppressed. The physical quantitysensor 1, the physical quantity detection circuit 200, or the method fordiagnosing failure of the physical quantity sensor 1 can therefore lowerthe influence of the detected physical quantity on the vibration leakagesignal QDOX, whereby the failure diagnosis can be performed on a regularbasis concurrently with the detection of the physical quantity.

In the physical quantity sensor 1 according to the present embodiment,the physical quantity detection circuit 200 includes the failurediagnosis circuit 60, which performs failure diagnosis based on thevibration leakage signal. The failure diagnosis circuit 60 thendiagnoses that the state of the physical quantity sensor 1 as failurewhen the magnitude of the vibration leakage signal QDOX does not fallwithin the first range. The physical quantity sensor 1, the physicalquantity detection circuit 200, or the method for diagnosing failure ofthe physical quantity sensor 1 can therefore reduce the processingburden on the MCU 5 because the MCU 5, which is an external apparatus,needs to perform no failure diagnosis. Further, when the first range isvariable, an appropriate first range according to the magnitudes of thefirst and second vibration leakage components is settable, whereby aconcern of wrong diagnosis performed by the failure diagnosis circuit 60is suppressed. Further, arbitrary one of a plurality of types ofphysical quantity detection device 100 that provide first and secondvibration leakage components having different magnitudes can be coupledto the physical quantity detection circuit 200 with no change in designof the physical quantity detection circuit 200.

1-7. Variations

For example, the physical quantity detection circuit 200 includes thefailure diagnosis circuit 60 in the embodiment described above but mayinclude no failure diagnosis circuit. For example, the MCU 5, which isan external apparatus, may diagnose failure of the physical quantitysensor 1 based on the vibration leakage signal QDOX.

In the embodiment described above, the physical quantity detectioncircuit 200 outputs the physical quantity detection signal SDOX and thefailure diagnosis result signal QF to the MCU 5, which is an externalapparatus, via the interface circuit 70 in accordance with a requestfrom the MCU 5 and may instead output the failure diagnosis resultsignal QF via the interface circuit 70 independently of the physicalquantity detection signal SDOX. Further, the physical quantity detectioncircuit 200 may output the failure diagnosis result signal QF not viathe interface circuit 70 but via an external terminal.

In the embodiment described above, the physical quantity detectioncircuit 200 outputs the physical quantity detection signal SDOX and thevibration leakage signal QDOX, which are each a digital signal, via theinterface circuit 70 and may instead output a physical quantitydetection signal and a vibration leakage signal that are each an analogsignal via an external terminal.

In the embodiment described above, the analog/digital conversion circuit41 converts the physical quantity detection signal SAO into the physicalquantity detection signal SDO, and the analog/digital conversion circuit42 converts the vibration leakage signal QAO into the vibration leakagesignal QDO, and one analog/digital conversion circuit may performconversion of the physical quantity detection signal SAO into thephysical quantity detection signal SDO and conversion of the vibrationleakage signal QAO into the vibration leakage signal QDO in a timedivision manner.

In the embodiment described above, the digital signal processing circuit51 performs predetermined computation on the physical quantity detectionsignal SDO to generate the physical quantity detection signal SDOX, andthe digital signal processing circuit 52 performs predeterminedcomputation on the vibration leakage signal QDO to generate thevibration leakage signal QDOX. One digital signal processing circuit mayinstead generate the physical quantity detection signal SDOX and thevibration leakage signal QDOX in a time division manner.

In the embodiment described above, the physical quantity sensor 1includes the physical quantity detection device 100, which detectsangular velocity as the physical quantity and may instead include aphysical quantity detection device that detects a physical quantityother than angular velocity. For example, the physical quantity sensor 1may include physical quantity detection devices that detectacceleration, angular acceleration, speed, force, and other physicalquantities.

In the embodiment described above, the physical quantity sensor 1include one physical quantity detection device and may instead include aplurality of physical quantity detection devices. For example, thephysical quantity sensor 1 may include a plurality of physical quantitydetection devices, and the plurality of physical quantity detectiondevices may each detect a physical quantity by using any one of two ormore axes perpendicular to one another as a detection axis. Further, forexample, the physical quantity sensor 1 may include a plurality ofphysical quantity detection devices, and the plurality of physicalquantity detection devices may detect any one of a plurality of types ofphysical quantity, such as angular velocity, acceleration, angularacceleration, speed, and force. That is, the physical quantity sensor 1may be a composite sensor.

The above embodiment has been described with reference to the case wherethe vibration element of the physical quantity detection device 100 is adouble-T-shaped quartz crystal vibration element, and the vibrationelement of a physical quantity detection device that detects a varietyof physical quantities may, for example, be a tuning-fork-type orcomb-type vibration element or a tuning-fork-type vibration elementhaving, for example, a triangular, quadrangular, or circular columnarshape. The vibration element of the physical quantity detection devicemay be made, for example, of a piezoelectric material, such aspiezoelectric crystal, such as lithium tantalate (LiTaO₃) and lithiumniobite (LiNbO₃), or piezoelectric ceramic, such as lead zirconatetitanate (PZT), or a silicon semiconductor in place of quartz crystal(SiO₂). The vibration element of the physical quantity detection devicemay, for example, have a structure in which a piezoelectric thin filmmade, for example, of zinc oxide (ZnO) or aluminum nitride (AlN) andsandwiched between the drive electrodes is disposed on part of thesurface of a silicon semiconductor. For example, the physical quantitydetection device may be a MEMS (micro electro mechanical systems)device.

In the embodiment described above, a piezoelectric physical quantitydetection device has been presented by way of example, and a physicalquantity detection device that detects a variety of physical quantitiesis not limited to a piezoelectric device and may instead be of anelectrostatic capacity type, an electro-dynamic type, an eddy currenttype, an optical type, a strain gauge type, and other types. Thedetection method employed by the physical quantity detection device isnot limited to a vibration-based method and may, for example, be anoptical method, a rotary method, or a fluidic method.

2. Electronic Instrument

FIG. 10 is a functional block diagram showing an example of theconfiguration of an electronic instrument according to the presentembodiment. An electronic instrument 300 according to the presentembodiment includes a physical quantity sensor 310, a processing circuit320, an operation section 330, a ROM (read only memory) 340, a RAM(random access memory) 350, a communication section 360, and a displaysection 370, as shown in FIG. 10. The electronic instrument according tothe present embodiment may instead be so configured that part of thecomponents shown in FIG. 10 is omitted or changed or another componentis added to the components shown in FIG. 10.

The physical quantity sensor 310 detects a physical quantity and outputsthe result of the detection to the processing circuit 320. The physicalquantity sensor 1 according to the present embodiment described abovecan, for example, be used as the physical quantity sensor 310.

The processing circuit 320 carries out a process based on the outputsignal from the physical quantity sensor 310. Specifically, theprocessing circuit 320 communicates with the physical quantity sensor310 and uses the output signal from the physical quantity sensor 310 toperform a variety of types of calculation and control in accordance witha program stored, for example, in the ROM 340. In addition, theprocessing circuit 320 carries out a variety of processes according toan operation signal from the operation section 330, the process ofcontrolling the communication section 360 for data communication with anexternal apparatus, the process of transmitting a display signal fordisplaying a variety of pieces of information on the display section370, and other processes.

The operation section 330 is an input apparatus formed, for example, ofoperation keys or button switches and outputs an operation signalaccording to a user's operation to the processing circuit 320.

The ROM 340 stores programs, data, and other pieces of information forthe variety of types of calculation and control performed by theprocessing circuit 320.

The RAM 350 is used as a work area where the processing circuit 320operates and temporarily stores the programs and data read from the ROM340, data inputted via the operation section 330, results of computationperformed by the processing circuit 320 in accordance with the varietyof programs, and other pieces of information.

The communication section 360 performs a variety of types of control forestablishing data communication between the processing circuit 320 andan external apparatus.

The display section 370 is a display apparatus formed, for example, of aliquid crystal display (LCD) and displays a variety of pieces ofinformation based on the display signal inputted from the processingcircuit 320. The display section 370 may be provided with a touch panelthat function as the operation section 330.

Using, for example, the physical quantity sensor 1 according to thepresent embodiment described above as the physical quantity sensor 310allows generation of a signal usable for the failure diagnosis based onthe leakage vibration that occurs at the physical quantity detectiondevice and reduction in the influence of the leakage vibration on thephysical quantity detection signal, whereby a reliable electronicinstrument can, for example, be achieved.

A variety of electronic instruments are conceivable as the electronicinstrument 300. Conceivable examples of the electronic instrument 300may include a personal computer, such as a mobile personal computer, alaptop personal computer, and a tablet personal computer; a mobileterminal, such as a smartphone and a mobile phone; a digital camera; aninkjet-type liquid ejection apparatus, such as an inkjet printer; astorage area network instrument, such as a router and a switch; a localarea network instrument, an instrument for a mobile terminal basestation; a television receiver; a video camcorder; a video recorder; acar navigator; a real-time clock apparatus; a pager; an electronicnotepad; an electronic dictionary; a desktop calculator; an electronicgame console; a game controller; a word processor; a workstation; a TVphone; a security television monitor; electronic binoculars; a POSterminal; a medical instrument, such as an electronic thermometer, ablood pressure gauge, a blood sugar meter, an electrocardiograph, anultrasonic diagnostic apparatus, and an electronic endoscope; a fishfinder; a variety of measuring instruments; a variety of meters for car,airplane, and ship; a flight simulator; a head mounted display; a motiontracer; a motion tracker; a motion controller; and a pedestrian deadreckoning (PDR) apparatus.

FIG. 11 is a perspective view diagrammatically showing a digital camera1300, which is an example of the electronic instrument 300 according tothe present embodiment. FIG. 11 also shows connection to an externalinstrument in a simplified manner. In a typical camera, a silverphotographic film is exposed to light, specifically, to an optical imageof a subject, whereas the digital camera 1300 converts an optical imageof a subject in a photoelectric conversion process by using an imagingdevice, such as a charge coupled device (CCD) and generates a capturedimage signal.

A display section 1310 is provided on the rear surface of an enclosure1302 of the digital camera 1300 and displays an image based on thecaptured image signal from the CCD. The display section 1310 thusfunctions as a finder that displays the subject in the form of anelectronic image. Further, alight receiving unit 1304 including anoptical lens, the CCD, and other components is provided on the frontsurface of the enclosure 1302. When a user of the camera checks thesubject image displayed on the display section 1310 and presses ashutter button 1306, a captured image signal from the CCD at that pointof time is transferred to and stored in a memory 1308. Further, in thedigital camera 1300, a video signal output terminal 1312 and a datacommunication input/output terminal 1314 are provided on the sidesurface of the enclosure 1302. A television monitor 1430 is coupled tothe video signal output terminal 1312 as necessary, and a personalcomputer 1440 is coupled to the data communication input/output terminal1314 as necessary. Further, in response to predetermined operation, thecaptured image signal stored in the memory 1308 is outputted to thetelevision monitor 1430 or the personal computer 1440. The digitalcamera 1300 includes the physical quantity sensor 310, which is, forexample, an angular velocity sensor, and uses the output signal from thephysical quantity sensor 310 to perform, for example, hand-shakecorrection.

3. Vehicle

FIG. 12 shows an example of a vehicle according to the presentembodiment. A vehicle 400 shown in FIG. 12 includes a physical quantitysensor 410, processing circuits 440, 450, and 460, a battery 470, and anavigator 480. The vehicle according to the present embodiment may be soconfigured that part of the components shown in FIG. 12 is omitted oranother component is added to the components shown in FIG. 12.

The physical quantity sensor 410, the processing circuits 440, 450, and460, and the navigator 480 operate by using power supply voltagesupplied from the battery 470.

The physical quantity sensor 410 detects a physical quantity and outputsthe result of the detection to the processing circuits 440, 450, and460.

The processing circuits 440, 450, and 460 carry out processes based onthe output signal from the physical quantity sensor 410. For example,the processing circuits 440, 450, and 460 use the output signal from thephysical quantity sensor 410 and perform a variety of types of controlof an attitude control system, a rollover prevention system, a brakesystem, and other systems.

The navigator 480 displays the position of the vehicle 400, the time,and a variety of other pieces of information on a display based onoutput information from a built-in GPS receiver. The navigator 480identifies the position and orientation of the vehicle 400 based on theoutput signal from the physical quantity sensor 410 even when noelectric waves from GPS satellites reach the navigator 480 and keepsdisplaying necessary information.

Using, for example, the physical quantity sensor 1 according to theembodiment described above as the physical quantity sensor 410 allows,for example, a reliable vehicle to be achieved because a signal usablefor the failure diagnosis can be generated based on the leakagevibration that occurs at the physical quantity detection device and theinfluence of the leakage vibration on the physical quantity detectionsignal can be reduced.

The thus configured vehicle 400 is conceivably any of a variety ofvehicles, for example, an automobile, such as an electric automobile, anairplane, such as a jet plane and a helicopter, a ship, a rocket, and anartificial satellite.

The embodiment and the variations described above are presented by wayof example, and the present disclosure is not limited thereto. Forexample, any of the embodiment and the variations can be combined witheach other as appropriate.

The present disclosure encompasses substantially the same configurationas the configuration described in the embodiment (for example, aconfiguration having the same function, using the same method, andproviding the same result or a configuration having the same purpose andproviding the same effect). Further, the present disclosure encompassesa configuration in which an inessential portion of the configurationdescribed in the embodiment is replaced. Moreover, the presentdisclosure encompasses a configuration that provides the sameoperational effect as that provided by the configuration described inthe embodiment or a configuration that can achieve the same purpose asthat achieved by the configuration described in the embodiment. Further,the present disclosure encompasses a configuration in which a knowntechnology is added to the configuration described in the embodiment.

What is claimed is:
 1. A physical quantity detection circuit thatreceives a first signal and a second signal outputted from a physicalquantity detection device that detects a physical quantity and generatesa physical quantity detection signal according to the physical quantitydetected with the physical quantity detection device based on the firstand second signals, the first signal containing a first physicalquantity component based on the physical quantity detected with thephysical quantity detection device and a first vibration leakagecomponent based on vibration of the physical quantity detection device,the second signal containing a second physical quantity component basedon the physical quantity detected with the physical quantity detectiondevice and a second vibration leakage component based on the vibrationof the physical quantity detection device, the first and second physicalquantity components having opposite phases, and the first and secondvibration leakage components having the same phase, the physicalquantity detection circuit comprising: a differential amplificationcircuit that differentially amplifies a signal pair based on the firstand second signals; an adder circuit that adds the signal pair; a firstsynchronous wave-detection circuit that performs synchronouswave-detection on a signal based on an output signal from thedifferential amplification circuit and outputs a signal according to adifference between the first physical quantity component and the secondphysical quantity component; a second synchronous wave-detection circuitthat performs synchronous wave-detection on a signal based on an outputsignal from the adder circuit and outputs a signal according to a sum ofthe first vibration leakage component and the second vibration leakagecomponent; a physical quantity detection signal generation circuit thatgenerates the physical quantity detection signal based on an outputsignal from the first synchronous wave-detection circuit; and avibration leakage signal generation circuit that generates a vibrationleakage signal based on an output signal from the second synchronouswave-detection circuit.
 2. The physical quantity detection circuitaccording to claim 1, wherein an amount of difference between the firstvibration leakage component and the second vibration leakage componentis substantially zero.
 3. The physical quantity detection circuitaccording to claim 1, further comprising: a first charge amplificationcircuit to which the first signal is inputted; and a second chargeamplification circuit to which the second signal is inputted, whereinthe signal pair is formed of an output signal from the first chargeamplification circuit and an output signal from the second chargeamplification circuit.
 4. The physical quantity detection circuitaccording to claim 1, further comprising a failure diagnosis circuitthat performs failure diagnosis based on the vibration leakage signal.5. The physical quantity detection circuit according to claim 4, whereinthe failure diagnosis circuit diagnoses a state of the physical quantitydetection circuit as failure when a magnitude of the vibration leakagesignal does not fall within a first range.
 6. The physical quantitydetection circuit according to claim 5, wherein the first range isvariable.
 7. A physical quantity sensor comprising: the physicalquantity detection circuit according to claim 1; and the physicalquantity detection device.
 8. An electronic instrument comprising: thephysical quantity sensor according to claim 7; and a processing circuitthat carries out a process based on an output signal from the physicalquantity sensor.
 9. A vehicle comprising: the physical quantity sensoraccording to claim 7; and a processing circuit that carries out aprocess based on an output signal from the physical quantity sensor. 10.A method for diagnosing failure of a physical quantity sensor includinga physical quantity detection device that detects a physical quantityand outputs a first signal and a second signal and a physical quantitydetection circuit that generates a physical quantity detection signalaccording to the physical quantity detected with the physical quantitydetection device based on the first and second signals, the first signalcontaining a first physical quantity component based on the physicalquantity detected with the physical quantity detection device and afirst vibration leakage component based on vibration of the physicalquantity detection device, the second signal containing a secondphysical quantity component based on the physical quantity detected withthe physical quantity detection device and a second vibration leakagecomponent based on the vibration of the physical quantity detectiondevice, the first and second physical quantity components havingopposite phases, and the first and second vibration leakage componentshaving the same phase, the method comprising: a differentialamplification step of differentially amplifying a signal pair based onthe first and second signals outputted from the physical quantitydetection device; an adding step of adding the signal pair; a firstsynchronous wave-detection step of performing synchronous wave-detectionon a signal based on a signal obtained in the differential amplificationstep to generate a signal according to a difference between the firstphysical quantity component and the second physical quantity component;a second synchronous wave-detection step of performing synchronouswave-detection on a signal based on a signal obtained in the adding stepto generate a signal according to a sum of the first vibration leakagecomponent and the second vibration leakage component; a physicalquantity detection signal generation step of generating the physicalquantity detection signal based on a signal generated in the firstsynchronous wave-detection step; a vibration leakage signal generationstep of generating a vibration leakage signal based on a signalgenerated in the second synchronous wave-detection step; and a failurediagnosis step of diagnosing failure of the physical quantity sensorbased on the vibration leakage signal.
 11. The method for diagnosingfailure of a physical quantity sensor according to claim 10, wherein anamount of difference between the first vibration leakage component andthe second vibration leakage component is substantially zero.
 12. Themethod for diagnosing failure of a physical quantity sensor according toclaim 10, wherein the physical quantity detection circuit includes afirst charge amplification circuit to which the first signal isinputted, and a second charge amplification circuit to which the secondsignal is inputted, wherein the signal pair is formed of an outputsignal from the first charge amplification circuit and an output signalfrom the second charge amplification circuit.
 13. The method fordiagnosing failure of a physical quantity sensor according to claim 10,wherein in the failure diagnosis step, a state of the physical quantitysensor is diagnosed as failure when a magnitude of the vibration leakagesignal does not fall within a first range.
 14. The method for diagnosingfailure of a physical quantity sensor according to claim 13, wherein thefirst range is variable.